I was invited to an employer before my interview was even scheduled. Is this a worthwhile use of my time?

One of the biggest mistakes a candidate can make is failing to attend the pre-interview functions and social events hosted by the company.  It is absolutely essential that you attend any and all events that might occur prior to the interview itself.
These events are designed to give company representatives, other than your interviewers, a chance to get to know you.  It is also your chance to make a shining impression on a great number of people.  If you fail to attend, your chances of receiving an offer will be greatly reduced.